Wells are generally drilled into the ground or ocean bed to recover natural deposits of oil and gas, as well as other desirable materials that are trapped in geological formations in the Earth's crust. Such wells are drilled using a drill bit attached to the lower end of a drill string. Drilling fluid (“mud”) is pumped from the wellsite surface down through the drill string to the drill bit. The drilling fluid lubricates and cools the bit, and may additionally carry drill cuttings from the wellbore back to the surface.
Well drilling techniques may utilize mud-pulse telemetry to communicate information between surface equipment and the bottom-hole assembly (BHA) and/or other downhole components of the drill string. For example, mud-pulse telemetry may be utilized to transmit commands and other information from surface equipment to a measurement-while-drilling (MWD) tool of the BHA. The MWD tool may include various sensors utilized to acquire data related to a subterranean formation, which may then be transmitted to the surface equipment via mud-pulse telemetry. Mud-pulse telemetry transmits information between the surface equipment and the BHA in the form of modulated pressure pulses that propagate through the drilling fluid circulated down through the drill string and BHA and back up to the surface through the annulus between the drill string and the wellbore.
The BHA includes various components that utilize electrical power. The electrical power may be generated downhole by a power generation module comprising a housing, an electrical generator within the housing, an impeller external to the housing, and a shaft extending through the housing between the impeller and the generator. Drilling fluid pumped through the drill string imparts rotation to the impeller, thus driving the electrical generator. However, the mud-pulse telemetry pressure pulses may cause pressure spikes that momentarily amplify the pressure differential across a fluid seal disposed between the shaft and the housing, thus permitting the drilling fluid to slowly leak into the housing through the seal. Such leakage may compromise the seal, hydraulic fluid within the housing, the electrical generator, and/or various other mechanical and/or electrical components within the housing.